The present invention utilizes supplemental heating to reduce particle generation in a deposition chamber such as a physical vapor deposition (PVD) chamber.
In a PVD process, a target material is placed within and electrically isolated from a vacuum chamber. A plasma stream is directed onto the target material where the plasma ions dislodge the target material. An electric potential between the target and a specimen attracts the dislodged target material to the specimen, and an even layer of target material coats the specimen.
For example, TiN is deposited as a barrier layer on each side of every metallization layer in semiconductor manufacturing. During the deposition process, TiN is deposited on every surface exposed to the sputtering field, not just to the wafer itself. In order to keep the deposition tooling chambers clean and particle-free, the deposition tooling includes shields that are placed within the deposition chamber to prevent any deposition on the chamber itself. After a number of cycles, the coatings deposited on the deposition shields begin to fracture and produce particles which can fall onto, and contaminate, the specimen. At this point, the manufacturing process must be stopped so the shields can be replaced. Since it takes at least a day to replace the shields and get the chamber back into condition for semiconductor processing, it would be very desirable to extend the number of cycles a chamber could run before particle generation causes the manufacturing process to be stopped.
Much effort has been undertaken to minimize the effects of particle generation from a shield.
U.S. Pat. No. 5,202,008 of Talieh et al. discloses a system where the shield is sputter-etch cleaned prior to use to increase adhesion of deposits by removing oxides which prevent deposits from bonding to the shield and by increasing surface roughness, which also increases the mechanical bonding of the deposits.
U.S. Pat. No. 5,630,917 of Goa describes a two-step chamber plasma cleaning process that is used because a baffle divides the chamber.
U.S. Pat. No. 5,598,622 of Raaijmakers describes a system where heating lamps normally used for chamber bake-out (removing moisture after the chamber is sealed) and mounted under a shield provide internal heating for expanding the shield to contact the inner walls of the deposition chamber, which prevents warping of the shield. The patent notes that excessive thermal expansion (changes in size during processing) may contribute to harmful contamination of the work piece. The patent teaches heating the shield from 50-300.degree. C. above the inner wall of the chamber to maintain contact. There is no teaching in this patent that maintaining the higher temperature may reduce contamination build-up. There is also no indication in this patent that Raaijmakers actually ever applied higher temperatures to his shield, as bake-out lamps are incapable of heating a shield beyond 100.degree. C. Furthermore, heating the entire chamber to 300.degree. C. would cause other difficulties with the manufacturing process.
This invention was conceived and tested in a vacuum chamber manufactured by the Assignee of U.S. Pat. No. 5,598,622. The Endura.TM. chamber of this Assignee includes a pair of quartz bakeout lamps installed horizontally inside the chamber. These lamps are cylinders installed parallel to each other on opposite sides of the chamber in a horizontal plane, directly under the outer edge of the lower shield. Power is supplied to the lamps during chamber idle, and varies from 0% to 100% of full power. Use of lamps relies on IR radiation which, by its nature, is line of sight. Shield parts which are not directly visible by the lamps are not heated directly. Those parts close to the lamps are heated very much. As discussed hereinafter, the invention provides a significant improvement over this prior art.